United States Office of Air Quality EPA-450/4-86-007 

Environmental Protection Planning and Standards July 1986 

Agency Research Triangle Park NC 27711 + 

Air 

>W

, EPA Guideline on the 

ldentificatiori and 

 Use of Air Qijality 

Data Affected by 

Exceptional Events 
a 

DISCLAIMER 

This report has been reviewed by the Office of Air Quality Planning and 

Standards, Environmental Protection Agency, and approved for publication. 

Mention of trade names or commercial products is not intended to constitute 

endorsement or recommendation for use. 

CM 

n 
EPA-450/4-86-007 

Guideline on the Identification 

and Use of Air QLiality Data 

Affected by Exceptional Events 

~ 

ri 

U.S. ENVIRONMENTAL PROTECTION AGENCY 

Office of Air and Radiation 

Office of Air Quality Planning and Standards 

Monitoring and Data Analysis Division 

Research Triangle Park, NC 27711 

July 1986 

~ 

CONTENTS 

r 

1. INTRODUCTION . . . . . . . . . . .. . . . . . . . . . . . . . 1 

2. PURPOSE AND MANAGEMENT OF FLAGGING SYSTEM . . . . . . . . . . 5 

2.1 Pre-Ai rs . . . . . . . . . . . . . . . . . . . . . . . . 5 

2.2 Post-Ai rs . . . . . . . . . . . . . . . . . . . . . . . 6 

3. USES OF FLAGGED DATA . . . . . . .. . . . . . . . . . . . . . 8 

.3.1 General Guidelines on the Use of Flagged Data ..... 8 

3.2 NAAQS Status . . . . . . . . .. . . . . . . . . . . . . . 9 

3.3 Trends Analysis . . . . . . . . . . . . . . . . . . . . 10 

3.4 SIP Regulatory Activities . . . . . . . . . . . . . . . 11 

4. DEFINITION AND APPLICATION OF EXCEPTIONAL EVENTS ...... 12 

4.1 Definitions of Exceptional Events . . . . . . . . . 12 

4.1.1 General Exceptional Event Criteria . . . . . . . 13 

4.1.2 Specific Definitions . . . . . . . . . . . . . . 14 

4.2 Demonstration of Causai Relation . . . . . . . . . . . . 24 

4.3 Application of Definitions and/or Criteria ....... 25 

4.4 Documentation . . . . . . . „ . . . . . . . . . . . . . 26 

APPENDIX . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . 28 

Development of Criteria for Possible Exceptional Events 

I. Identification of Events . . . ,. . . . . . . . . . . . . . 28 

II. Events Not Considered Exceptional for Data Flagging 

Purposes . . . . . . . . . . . . . . . . .... . . . . . . . 31 

s 

REFERENCES . . . . . . . . . . . . . . . ,; . . . . . . . . . . . . . 34 

ii 
a .X 
a 

SECTION 1 

INTRODUCTION 

Federal, State, and local air pollution control officials have expressed 

a great deal of concern rega'rding the handling of air quality data that are 

influenced by both natural and man-made event:s that are considered exceptional. 

These events are considered exceptional for two reasons; they are not expected 

to recur routinely at a given location, or thiay are possibly uncontrollable 

or unrealistic to control through the State Implementation • Plan (SIP) process. 

In some cases in the past, air quality data collected during these "exceptional" 

events have not been submitted to the National Air Data Bank (NADB) because 

State or local agencies were concerned about 'the potential misuse of such 

data. This guideline document was prepared as a response to this concern and 

is intended to provide national guidance for identifying ("flagging") and using 

ambient air quality data influenced by except lional events. 

The guidance includes definitions of 18 acceptable exceptional events 

and describes the procedures for submitting f'lagged data influenced`by these 

events to EPA's Aerometric Information Retrieval System (AIRS). The Appendix 

provides information on other events which were also initially proposed for 

consideration as "exceptional" but are not included in the final flagging 

system. 

The need for a flagging (or "identification") system was implied in 

previous Agency guidelines and regulations. 'The first example is Office of 

Air Quality Planning and Standards' Guideline No. 1.2-008 (revised February 

~ 1977) entitled, "Guidelines for the Interpretation of Air Quality Standards." 1 

1 

■ 
At 

This guideline addressed the submission and use of - all valid air quality data 

for determining an area's overall compliance status with respect to National ~ 

Ambient Air Quality Standards (NAAQS). Issue 9 in the guideline posed the 

following question: "How should particulate matter (PM), carbon monoxide 

(CO), and other pollutant concentrations resulting from severe recurring dust 

storms, forest fires, volcanic activity, and other natural sources be taken 

into account in determining compliance with NAAQS?" The guideline recommended, 

"° Regardless of the source, ambient pollutant concentrations exceeding a NAAQS 

constitute a violation." The guideline, however, implied a need for data 

flagging by further stating, "Detailed information establishing that viola- , 

tions are due to uncontrollable natural sources may be used in determining 

the feasibility of modifying control strategies." 

The second example is in 40 CFR 51.12 (d), the regulations for the 

development, adoption, and submittal of SIP's. 2The regulations stated: "For 

purposes of developing a control strategy, data derived from measurements of 

existing ambient levels of a pollutant may be adjusted to reflect the extent 

to which occasional natural or accidental phenomena, e.g., dust storms, 

forest fires, industrial accidents, demonstrably affected such ambient levels 

during the measurement period." 

A third example is provided in the March 20, 1984, 40 CFR Part 50 

Federal Register proposed revisions to the national ambient air qual,ity standards for particulate matter. 3Appendix K of Part 50 would allow consideration 

of the influence of rare or unusual events on PM10 data by various techniques. 

Pa 
A11 three examples, OAQPS 1.2-008, 4.0 CF'R 51.12(d), and the proposed 

A 

40 CFR 50 Appendix K reflect concern that sonie air quality data associated 

, with the occurrence of certain types of event':s may require special 

consideration in order to avoid misuse. 

The guideiine's general policy is to alliow consideration of excluding 

flagged data from use in regulatory actions. The actual exclusion of the use 

of flagged data would only be allowed if, as a result of a public review 

process, the responsible government agency e„g., the State Air Agency during 

the State regulatory process, and the U. S. EPA during the Federal review/ 

approval process, determines that the data are inappropriate for use in a 

specific regulatory activity. This consider<ition for exclusion of flagged 

data carries with it no prior presumption towards use or non-use of flagged 

data. 

By establishing uniform procedures and criteria for flagging and 

determining the use of data associated with exceptional events, EPA expects 

data collectors to submit to the NADB - aII va'lid ambient air quality data, 

i.e., data collected in accordance with 40 CFR 58. Having a complete national 

air q-uality data file will provide a data base adequate to evaluate and 

substantiate the impact of exceptional events on air quality and to assist 

users in interpreting the data. 

The guideline provides criteria and procedures by which potential users 

of air quality data can be informed of "excelitional events" which may have 

influenced the data. The guideline has no riegulatory or legal significance 

regarding use of any air quality data. Use or non-use of air quality data, 

whether flagged or not, must be subjected to full public disclosure and 

rulemaking procedures. 

3 
The criteria for identification of "exceptional events" are designed to 

be expansive enough to encompass most good faith claims by State and local 

agencies of when data should be considered for special treatment. It is not 

intended to reflect EPA's views on the validity of these claims. The flagging 

of data is merely a way for a State or local agency to state that it regards 

the data as influenced by exceptional events, and may later claim that the 

data should be discounted for certain purposes. 

As experience with this guideli-ne is gained, periodic revisions may be 

made. The guideline is to be implemented on a trial basis for approximately 

2 years, after which the Standing Air Monitoring Work Group (SAMWG) will 

assess its effectiveness and make any appropriate recommeridations for revision. 

The SAMWG is composed of Federal, State, and local air pollution control 

officials who constitute a forum for discussion and resolution of ambient air 

quality monitoring issues. 

A 

9 
SECTION 2 

PURPOSE AND MANAGEMENT OF THE FLAGGING SYSTEM 

The basic purpose of the flagging system is to identify those air quality 

measurements that are influenced by exceptional events. These are events 

which, if unidentified, could lead to possible misinterpretation or misuse of 

the data. Because the fiagging system relies heavily on the identification 

and understanding of events that may have influenced a particuiar air quality 

measurement, its major thrust is information ,exchange. If a particular air 

quality measurement is influenced by an exceptional event, it is important 

for all those who may review and ultimately use the data to be aware of this 

influence and to take care that such data are not misinterpreted or misused. 

Knowledge and understanding of what the data represent are critical in the 

overall air quality planning process. 

Under the flagging system, State and local air poliution control agencies 

will be responsible for initially identifying and documenting data influenced 

by exceptional events. These agencies also must develop the appropriate background information used to support the decision to flag an individual piece 

of data; they must submit the information to EPA for concurrence and make it 

available for the public°s review upon request. Because of the potential 

implications on the use of flagged data, the agency flagging the data must 

(as discussed in Section 4.2) clearly demonst;rate a causality between the 

exceptionai event and the flagged air qualityl data. 

2.1 PRE-AIRS PROCEDURES 

- Until the Aerometric Information Retrieval System (AIRS) is operational, 

the flagged data should be specifically identified and discussed in the 

5 1 
annual State and Local Air Monitoring System (SLAMS) Report. The EPA Regional 

Offices will be responsible for review and concurrence or non-concurrence with 

the flag, except for data related to stratospheric ozone intrusions which 

will be reviewed and concurred or non-concurred with by OAQPS. States should 

initiate discussions with EPA Regional Offices regarding data that may be 

flagged as soon as possible after data collection, and should not wait until 

the annual SLAMS Report is submitted. 

2.2 POST-AIRS PROCEDURES 

After AIRS is operational, all flagged data will be entered and storeci 

in the AIRS; and as data are retrieved, a user will be able to identify those 

data that have been flagged. Each exceptional event will be assigned a 

unique flag code by the AIRS for the exceptional events included in this 

guideline. The procedure for submitting, reviewing, and assigning appropr -iate 

flags for data identtified by State or local agencies to be associated with an 

exceptional event are as follows: 

(1) The State or local agency should submit their flagged data with the 

proper unique flag code to AIRS as part of their routine data submissions i:o 

EPA's data bank. 

(2) The State or local agency should provide to the Regional Office, 

within 30 days, appropriate documentation and demonstration of causality as 

discussed in Section 4.4. 

(3) The Regional Office should concur or non-concur with the data flag 

and notify the State or local agency within 30 days of receipt of documentation from the agency. If the Regional Office concurs with the flagging of , 

the data, they will change the unique flag code associated with the data to 

~ 
a 

designate EPA Regional Office concurrence wi - th the flag. If the Region non- 

• concurs with the data.flag, the State or local agency flag will remain in 

AIRS with the particular data point. The non-concurrence by the Regional . 

Office could be revised upon subsequent submission of adequate justification 

by the State and local agency. The exception to the procedure is stratospheric 

ozone intrusion, which is to be reviewed and acted upon by OAQPS rather than 

the Regional Office. 

(4) Those States electing to submit to;NADB only an annual SLAMS report 

rather than raw data should include a section in their annual report which 

lists all flagged data, SAROAD I.D., date of occurrence, and type of acceptable 

exceptional event. 

Notification must be sent to AIRS and the Regional Office by the 

responsible State or local agency when flaggEad data are to be changed to a 

nonflagged status for any reason. 

Two data records will be maintained in AIRS. One record will contain 

all the data including the flagged data, and,the other will contain only 

data that have not been flagged. A11 users of the data will have access to 

both records, including the rationale for the flag and the EPA Regional 

Office concurrence or non-concurrence with ttie flag. 

7 
, ,.1 
SECTION 3 

USES OF FLAGGED DATA 

3.1 GENERAL GUIDELINES ON THE USE OF FLAGGED DATA 

Concern over the potential for misuse h'as made some State and local 

agencies reluctant to submit air quality data that were influenced by what 

they consider to be an exceptional event, i.e., an event that is not expected 

to recur routinely at a given location, or that is possibly uncontrollable 

or unrealistic to control through the State Implementation Plan (SIP) process. 

The views of Federal, - State, and local agency officials have varied concerning 

the use of air quality data collected during,an exceptional event. Some 

believed that air quality data collected during an exceptional event should 

not be used under any circumstances; some believed that all valid (i.e., collected in accordance with 40 CFR 58) data shiiuld be used (without exception); 

some believed that the data should be used oiily to determine the status of 

the area with respect to the NAAQS; and stil'I others believed that the data 

not only should be used to determine the compliance status of the area, but 

also to develop trends analyses and control <,;trategies (with some qualifications). This document addresses these differ°ences by requiring the States 

(and EPA) to identify and explain the use or non-use of data influenced by 

exceptional events during a public review prcicess. Furthermore, the guidance 

provided does not dictate any prior presumption toward use or non-use for any 

specific purpose. 

v In general, decisions on the use or non=.use of flagged data will be made 

.. , . 

t on a case-by-case basis for specific purposes; (attainment designations, control 

strategies, etc.), and the public rnust be inf- ormed that the data exist, whether 

N 
the data are used or not. The main concern lies with understanding what the 

flagged data represent. Three steps usually should be taken in order to 

decide whether questionable data should be flagged, and to assist potentia1 

users in determining how the data should be used. The first step is to determine the portion of the measured air quality level attributable to the sinc3le 

event, as well as the cumulative effect of several similar exceptional everits, 

that create substantial impacts at a monitoring site. In some cases, mode1ing 

(either source apportionment or dispersion) or other procedures may be used to 

determine the relative contribution of the event. The relative contribution of 

the event provides a better understanding of what the air quality level for the 

day or days in question actually represents. 

The second step is to determine the area influenced by the event. In 

most cases, the impact will be limited. Therefore, if the data are being c:onsidered for use in or exclusion from regulatory purposes, the agency should 

determine the area which would be influenced by the determination. 

The third step is to demonstrate how the flagged data relate to data 

previously collected at the monitoring site. This step is extremely critical 

for trends analyses and for preparing reports to the public on air quality 

levels for a given area. Obviously, if flagged data are used or excluded - in 

preparing summaries of air quality data, the reader should be made aware of how 

the data were used. 

3.2NAAQS Status 

NAAQS compliance status involves the use of data to determine whether the 

• area represented by the data is meeting or exceeding the NAAQS for the pol1utant 

being monitored. It is EPA's policy and a regulatory requirement to have valid ' 

9 
NAMS and SLAMS data (i.e., data collected in'accordance with 40 CFR 58) 

. 

submitted to the NADB or included in the annual SLAMS report. A11 data, 

~ flagged or unflagged, should be avaiiable to the public for comparison to the 

NAAQS to determine if exceedances have occurired. A11 relevant flagged data 

along with the reasons for flagging, and a diemonstration of causality between 

the exceptional event and the flagged data, shall be submitted for consideration of use/non-use during any public hearin ~~ or comment period called under 

Sections 107, 110-113, 119, 120, 122, 123, 126, Part C or Part D of the Clean 

Air Act. 4 Consideration of ambient air qua'lity data during public reviews 

called under the authority of other sections or titles of the Clean Air Act, 

although not prohibited, does not appear to be relevant to the purpose of those 

reviews. For example, consideration of ambii~nt data at a hearing held regarding 

automotive emissions standards may or may noi: be appropriate. Such consideration 

is neither mandator.y nor prohibited. 

3.3 Trends Analysis 

Trends analysis involves the evaluation of 'the long-term trends associated 

with the measured levels of a given pollutani: for a given area. These analyses 

are useful in evaluating the overall progress of the air pollution control program for the given pollutant and in understariding why the concentration levels 

of a pollutant are increasing or decreasing. 

In some cases the data collected during'an exceptional event can be 

used for trends analysis (as long as the analyst understands the limitations 

, associated with the data). The trends analyses should clearly state how the 

flagged data were treated and to what extent the flagged data were or were 

` not included in the analyses and why. The tr•ends analyses also should consider 

10 
(to the extent possible) what effect the flagged data have on the overall 

trend line for the area in light of other confounding variables that may also 

affect the trend line. 9 

3.4 SIP Regulatory Activities 

The use of flagged air quality.data for SIP regulatory activities 

(areawide or local control strategy development, SIP design values, attain-• 

ment/non-attainment status, enforcement actions, etc.) shall be considered on 

a case-by-case basis and discussed during the public review process. Excliasion of the flagged data would only be allowed if the responsible control 

agency determines in conjunction with a public review that the flagged 

data are inappropriate for use. 

0 

11 
SECTION 4 

DEFINITION AND APPLICATION OF EXCEPTIONAL EVENTS 

4.1 DEFINITIONS OF EXCEPTIONAL EVENTS 

This guideline provides general definit'ions for these events and general 

criteria for their use in flagging air qualii:y data. The application of a 

definition may vary frorn area to area because of differing air quality and. 

control situations. For example, salting anci sanding of streets for snow and 

ice control rnay be an exceptional event in ttie southern sections of the country, 

whereas they may be routine, controllable events in the northern sections. 

Therefore, the following definitions are only a na -tional guide and are not 

meant to replace reasonable judgment on theFiart o -P the Regional, State, and 

local air pollution control agency officials in defining and identifying 

exceptional events for the purpose of flaggirig data. 

In situations where it can be shown that: the national criteria are 

generally inappropriate, a State Agency may propose alternate criteria to their 

EPA Regional office. These proposals would hiave to be subjected to public 

review within the State. The Regional office would be responsible for review 

and preliminary approval of the alternative criteria. The OAQPS wili have 

final approval authority and if approved, will include the alternative criteria 

as a supplement to this national giaideline. 

With the above limitations in mind, the following general definitions have 

been developed to promote consistency with respect to flagging data that have 

 been collected during an exceptional event. Whenever possible, specific criteria or terms have been used to define the event to minimize inconsistent 

interpretations. Of course, no term can be absolutely defined so that there is 

12 
no room for interpretation. Thus, these definitions and associated criteria 

provide for some flexibility in their application to an individual event. a 

What may be unusual or exceptional for one part of the country may be typical 

for another and this variability requires flexibility in national definitions ` 

and criteria. 

The definitions that follow have in some cases specific numbers included 

within the definition. Although they are not fully supported by technical 

studies, they are included as a practical alternative to deleting weakly supported values and, to the extent possible, reflect the comments received during 

development of this guideline. These numbers rnay require adjustments as 

experience is obtained with the guideline. 

4.1.1General Exceptional Event Criteria 

Before one can define an individual exceptional event, one must have a 

general definition of "exceptional." In a sense, this definition also serves 

as an overriding criterion with regard to the specific definitions presented 

in 4.1.2. 

Webster defines "exceptional" as forming an exception, rare, uncommon, 

extraordinary, deviating from the norm. With respect to air quality considerations in this guideline, an exceptional event is defined as an event that is 

not expected to recur routinely at a given location, or that is possibly uncontrollable or unrealistic to control through the SIP process. As noted previously, 

what is exceptional in one area of the country may not be ex :eptional in another. 

Therefore, some judgment is needed in identifying whether an event is exceptional 

in the area of the country where it has occurred. 

13 
. 4.1.2Specific Definitions 

The following definitions are provided'for the purpose of identifying 

an exceptional event. Some additional discussion is provided in each case 

to aid in the application of these definitions. 

HIGH WINDS (PM) 

Definition: 

An hourly windspeed of greater than or equal to 30 mph or gusts 

equal to or greater than 40 mph, with no precipitation 5 , 6or only 

a trace of precipitation (observed as scattered drops that do not 

completeiy wet or cover an exposed area up to a rate of 0.01 

inch/hr. 7 ). , 

The high wind condition with no precipi'tation or only light precipitation 

and dry soil must be associated with a significant contribution (estimated to 

be > 85% by weight) of crustal material on the PM sampling medium. High winds 

without unusually high PM levels due to the.'suspension or resuspension of 

crustal material should not be considered an'.exceptional event. Additionally, 

fugitive emissions or dust from any part of an industrial source should not be 

fl agged. 

STRATOSPHERIC OZONE INTRUSION (03) 

Definition: 

A stratospheric ozone intrusion occurs when a parcel of air 

originating in the stratosphere, ayerage height 20 km (12.4 mi), 8 

is entrained directly to the surface of the earth. 

` Although this event is exceptional, the circumstances or the criteria 

under which it occurs are difficult to measure or document given current 

L4 
measured meteorological parameters. Stratospheric ozone intrusions are 

infrequent and very localized events of short duration, which makes it difficult to use currently available airport data to determine whether a str<ito- ^ 

spheric ozone intrusion has occurred. Stratospheric ozone intrusions are 

typically associated with strong frontal passages or severe thunderstorms and, 

thus, may occur primarily during the spring of the year. The above defin -ition 

is provided only as a general guide for differentiating between stratospheric 

ozone intrusion, which is an exceptional event for the purpose of flagging 

data, and other nonexceptional meteorological events. Although data have been 

identified in the past as being the result of stratospheric ozone intrusion, no 

standard definition or criteria have been established for concrete identi - Fication. Therefore, determining whether a stratospheric ozone intrusion has 

occurred should be a case-by-case decision based on reasonable judgment regarding 

the season of the year, time of day, and accompanying meteorological conditions 

associated with the ozone measurement in question. The EPA concurrence or 

non-concurrence authority for flagging of ozone data for stratospheric in - trusion 

is the responsibility of OAQPS upon review of the documentation submitted by 

the State or local agency flagging the ozone data. 

VOLCANIC ERUPTIONS (CO 3 S02., NOp, PM) 

Definition: 

The emission or ejection of volcanic materials at the Earth's 

surface from a crater or fissure. 9 

Emissions from volcanic eruptions have a large-scale areawide impact on 

air quality. Excessive air quality concentrations resulting from volcanic 

eruptions should be flagged regardless of the frequency of eruptions. In most 

15 
! 

' cases, however, the eruptions and resulting impact on air quality would be 

very infrequent. 

SANDBLASTING (PM) 

Definition: 

Sandblasting or gritblasting refeirs to the temporary use of 

abrasive blasting with pressurizeci air for surface preparation 

purposes at a given location. 

Methods currently available are used tci control these operations to 

minimize their impact on air quality at fixed point sources where routine 

applications are part of the facilities' operations. Ambient air quality 

levels influenced by these activities shoulci not be fiagged. However, 

completely effective controi techniques are not necessarily available or 

possible for portable sandblasting operatioris. Therefore, data collected at 

a site within a micro or middle scale distance from a temporary (generally 3 

weeks or less) sandblasting operation may be flagged if all reasonable control 

measures have been employed to minimize adve!rse impacts on air quality. 

FOREST FIRES (CO 3PM) 

Definition: 

An uncontrolled fire in vegetation or associated flammable material 

that requires suppressive action to protect natural resources or 

values associated with natural resources or that is destructive to 

} natural resources. 10 

[E., 
Class Size, acres Class Size, acres 

A <0.25 D 100 - 299 

B 0.26 - 9 E 300 - 999 

C 10 - 99 F 1000 - 4999 

G >5000 

Some forest fires are unpreventable and because uncontrollable emissions 

from Forest fire can adversely affect air quality concentrations ov.er a large 

area, forest fires should be considered an exceptional event for the purpose of 

flagging air quality data. In general, Class A and B fires tend to have a morz 

loca1ized impact; therefore, only data collected at downwind monitors within 3 

miles of these type fires should be flagged. For Classes C through G, the 

impact of the fire is more widespread and the location with resppct to the 

monitor should be supported by receptor11 , 12 , 13 , 14 or dispersion modeling. 15 , 16 

STRUCTURAL FIRES (CO 3 PM) 

Definition: 

Any accidental fire involving some kind of structure. In 

' general, a structural fire involves a building having at 

least 600 square feet. 

The structural fire should be within a micro- or middle-scale distarrce (up 

to 500 meters as defined by 40 CFR 58, Appendix D) of a monitor in most instances 

for the data from that monitor to be flagged. However, a much greater distance 

may be appropriate for large fires such as a refinery, industrial, or commercial 

business area fire provided the causal relation is supported by receptor or 

dispersion modeling. 

17 
HIGH POLLEN COUNT (PM) 

k Definition: 

A pollen count index above 25 grains/cm 2or 1000 grains per 

1~ 

cubic meter. 17 

The pollen count index is usually obtained by use of a coated slide 

mounted on a circular plate that is generally mounted on the top of a seven 

or eight-story building with an unobstructed'air flow. The index is in units 

of grains of pollen per cm. 2Another method,of ineasuring the concentration 

of pollen is volumetric, i.e., counting the riumber of grains per cubic meter. 

Other recoqnized methods for measuring polleri levels may be used. For a 

high-pollen count to be flagged as an exceptional event, the pollen count 

index should be greater than 25, or 1000 grains per cubic meter and the highvolume filters on which the samples were collected should be analyzed micro- 

, scopically to ensure that significant amounts. of pollen (i.e., 50% or greater 

than the normal pollen count for a typical sa:mple) were collected on the day 

or days being considered for flagging. Where high pollen is considered to be 

a problem, State or local agencies should develop procedures for ascribing 

the effects of high pollen count on filters and should submit them to the 

respective Regional Office for approval. 

CHEMICAL SPILLS AND INDUSTRIAL ACCIDENTS (CO 3S02, NO2, PM) 

Definition: 

Emissions that result from accident`s such as fire, 

explosions, power outages, train derailment, vehicular 

accidents, or combinations of these. 18 

The spill or accident must, of course, n6t be a routine occurrence. Any 

of these situations that do occur routinely should be critically evaluated and 

18 
stopped. Data from sites that can be unequivocally related to a non-rout'ine 

accident or spill may be flagged. ' 

UNUSUAL TRAFFIC CONGESTION (CO) 

Definition: 

A condition resulting frorn a major accident (rather than 

frequent minor accidents,) or short-duration obstruction, 

such as demolition or construction. During these conditions 

the level of traffic may increase until it exceeds the 

maximum capacity of a given street or highway. Speeds are 

reduced substantially and stoppages may occur for short or 

long periods of time because of downstream congestion. In 

extreme cases, both speed and volume can drop to zero. 19 

As a general rule of thumb, congestion must occur'within five hundred 

meters of a monitoring site (i.e., micro- to middle-scale) and not be a regular 

occurrence for the data from that site to be flagged. 

CONSTRUCTION/DEMOLITION (PM) 

Definition: 

The building/destroying/renovation of any residential, 

institutional, commercial, or industrial building (including 

apartment buildings with more than four dwelling units), 

structure, facility, or installation that lasts for only a 

short period of time.and is reasonably controlled. 

The construction or demolition activity must take place within a reasonable • 

distance of the monitoring site and all reasonable control measures must be 

19 
in use before the data from the site can be flagged. Flagged data should be 

limited to sites classified as micro- or middie-scale (up to 500m) and downwind 

' with respect to the construction activity. 

AGRICULTURAL TILLING (PM) 

Definition: 

The act of preparing dry soil for cultivation or for 

controlling the growth of weeds by the use of inechanical 

devices during periods with an hourly average windspeed 

of greater than 20 mph. 

Generally, agricultural tilling operat - ions must occur within a reasonable 

distance (500 meters) of the monitoring sitE~ and tilling must have occurred at 

the same relative location while the hourly average windspeed is greater than 

20 mph for the monitoring data to be flaggeci. Flagged data must have been 

collected during or immediately after-the d<iy tilling occurred and should be 

limited to sites which would be classified <is micro- or middle-scale with 

respect to the tilling operations. 

HIGHWAY CONSTRUCTION (PM) 

Oefinition: 

The act of building a new, or repairing an existing, 

highway, road or street. 

Particulate matter resulting from reascinably controlled highway 

construction for short time periods may be f'lagged provided that a microscopic 

r. 

analysis of the filter indicates that 85 per-cent of material on the filter is 

~ related to construction activities and all reasonable control measures have 

been utilized. 

. ~ 

20 

m 
REROUTING OF TRAFFIC (CO) 

Definition: 

A temporary deviation or detour of vehicular traffic A 

because of an accident, construction, or demolition. The 

detour must be for no more than 1 week. 

The rerouting of traffic should be within a reasonable distance of a 

monitoring site and last for no more than 1 week for the monitoring data - to 

be flagged. Flagged data should be limited to sites classified as micro- or 

middle-scale (within 500 meters) with respect to the detour. 

SALTING/SANDING OF STREETS (PM) 

Definition: 

The application of salt and/or sand to the road surface to 

increase traction and/or prevent the surface water from 

refreezing after it has melted. 

The salting and sanding must occur within a reasonable distance (up to 

500 meters) of the monitoring site if the data from the site are to be flagged. 

Flagged data should be limited to sites classified as inicro- or middle-scale 

with respect to the salting/sanding operations and microscopic examination 

shows that 85 percent of the ►naterial on the filter is salt and/or sand. Data 

collection is not limited to the date of salting or sanding of the street. 

A11 reasonable control measures must be taken to minimize the adverse air 

quality impact of the salting or sanding operations in order for the data to 

be flagged. In general this type of data should not be flagged in areas , 

which experience a significant use of salt and/or sand. 

21 
i 

. INFREQUENT LARGE GATHERINGS (CO 3PM) 

Definition: 

A gathering of more than 10,000 people (5000 cars) at any 

one time and at a single iocation. Unusual traffic congestion 

must be associated with the event. 

A large gathering in and of itself wit'out the associated traffic 

congestion would not qualify as an unusual e!vent i`or the purpose of flagging. 

(See discussion of unusual traffic congestion for more details on the criteria for flagging data because of unusual traffic congestion). The event 

would also be expected to occur less than once per year, and the event should 

be at a location not regularly used for such purposes. Flagged data should be 

limited to sites classified as micro- or middle-scale with respec.t 'to the 

gathering. 

ROOFING OPERATIONS (PM, S02) 

Definition: 

The process of building, repairing, or recoating the external 

upper covering of a house or building that involves the 

application of a petroleum-based materia] (usually heavy 

residuals from a refining operation) to a roof. The material 

is heated and then sprayed or rolled onto the surf ace. 

Generally, a roof so covered wouldbe resurf aced or treated 

no more than once every 3 to 5 years. Uniess major damage 

has occurred, some surfaces would r~equire treatment oniy every 

„ 5 to 10 years. 

22 
Roofing operations must occur within a micro-scale distance and upwind 

of the monitoring site, and all reasonable control measures must be applied . 

for the data to be flagged. 

PRESCRIBED BURNING (PM, CO) 

Definition: 

A controlled fire of vegetative material that is used 

to improve range lands, agricultural or forestry resources, 

or associated values. 

Prescribed burning is generally a controlled activity that is 9imited to 

those days or periods when the meteorological conditions are conducive to good 

dispersion. Thus, the emissions which affect air quality are dispersed to the 

extent possible. However, the resulting emissions occasionally adversely affect 

air quality concentrations over a large area. In areas of the country-where 

prescribed burning is used regularly and extensively for agricultural and/or 

forestry land management, prescribed burning may not be considered an exceptional event for the'purposes of flagging air quality data. Prescribed 

burning in these areas is usually subject to rules and regulations, inclucling 

smoke management plans, under which a regulatory agency permits burning ai'ter 

deciding where, and to what extent, the smoke will be allowed to impact air 

quality. 

However, in many areas of the country, prescribed burning for agricultural, 

forestry land management, or other purposes is an infrequent but necessary 

activity and may be iinpractical to fully control. These practices may be conri 

sidered an exceptional event for the purposes of flagging air quality dat<i. 

23 
However., it must be demonstrated through reci'2ptor or dispersion modeling, 

A that the burning operations have a substantial impact on the monitored air 

quality data. 

CLEAN UP ACTIVITIES AFTER A MAJOR DISASTER (PM, CO, SO?) 

Definition: 

For the purposes of flagging, majoi ~ disasters are serious 

public misfortunes for which Statelor Federal relief has 

been granted. 

PM, CO 3S02 or other pollutant data affected by and collected during, or 

for a reasonable period after, the clean up <ictivities following a major 

disaster may be flagged. 

4.2 DEMONSTRATION OF CAUSAL RELATION 

Excluding the use of valid air quality clata from regulatory purposes 

is a serious action. Accordingly, a clear•demonstration of the relationship 

between the exceptional event and the measurEtd air quality must be provided. 

As a minimum, this demonstration should: (a) inciude all relevant raw data 

(e.g., air quality data, meteorological data„ traf-Fic counts, etc.); (b) show 

that the monitor did not record high concentrations before and after the 

~ period of the exceptional event; (c) show th<<t the local wind direction was 

such that the monitored pollutant was transpcirted from the exceptional event 

source to - tiie" moni tor duri ng the peri od i n questi on'; ( d) i nci ude as appropriate receptor 11 , 12 , 13 , 14 or dispersion mode;ling 15 , 16 connecting the monitored 

> concentrations with the exceptional source erriissions; (e) include, as appropriate, microscopic filter analyses (for part,iculate emissions); and (f) 

Y 

include documentation supporting the existence of the exceptional event. 

~ 

24 

~ 
t 

~ ~ ! 

4.3 APPLICATION OF DEFINITIONS AND/OR CRITERIA 

._ 

As noted earlier, the purpose of this guideline is to provide guidance 

and direction for flagging air quality data associated with exceptional I 

events and thus promote national consistency in the flagging of such data. 

Having established general definitions for the exceptional events arid 

the criteria for applying flags to the data, the State or local agency should 

consider flagging of any data meeting the criteria of this guideline and 

prepare adequate evidence to clearly demonstrate the causal relationship 

between the exceptional event and the flagged data. The flagged data with 

adequate documentation of the causal relationship should be submitted to the 

appropriate Regional Office following the procedures outlined in Sections 2.1 

and 2.2. The Regional Office, after review, should notify the State or local 

agency of any disagreements, their reasons for disagreeing, and seelc to resolve 

the conflict. Following their•determination (concurrence or non-concurrerice), 

the Regional Offices should notify AIRS and the State or local agency of their 

action so that the appropriate notation may be made to the AIRS data*base 

and/or the Annual SLAMS Report. 

The only exception to this policy is the flagging of stratospheric olone 

intrusion. 3ecause of the technical complexity of determining stratospher•ic 

ozone intrusion, OAQPS will, upon request by the State or local agency tnrough 

th°e°Regional Office, either concur or non-concur based on documentation 

submitted by the requestor. 

The criteria (definitions) presented in this guideline will serve as the 

1 

basis for reviewing determinations associated with exceptional events. If a 

State or local agency chooses to apply criteria that are less stringent than ~ 

those contained in the guideline, such recommendation should be subjected 

25 
~ 

to public review. The recommendation, aloncj with the summary of comments, 

should then be submitted to the respective F;egional Office for review and 

' approval. OAQPS will have final approval auithority and, if approval is granted, 

wili include the alternative criteria in a supplement to this national guideline. 

4.4 DOCUMENTATION 

A11 decisions regarding the flagging of` data because of exceptional 

events must be documented so that the EPA and the public can review these 

decisions. The documentation may take sever-al forms. It may include reports 

from the National Weather Service; a copy of' a newspaper clipping or news 

report indicating that a chemical spill or i,ndustrial accident has occurred; a 

report from the local health department on the pollen count for a given day, 

supported by fiiter analyses; special reports prepared by the State or a consultant; or special statistical analyses of 'the air quality data and other 

key parameters associated with the event. The actual form of the documentation 

depends on the event and the extent of publicly available reports or documents 

that would support the determination of its',occurrence. As appropriate, the 

State or local agency is encouraged to rely on available reports and documentation. When such documentat7on is not available 9the State or local agency 

must prepare the necessary material sufficient (see Section 4.2) to support 

its decision regarding the flagged data. 

The State or local agency should retain' copies of the necessary supporting 

materiai or documentation in its offices for review upon request. Copies of 

this material will have to be available in the record during the public 

review process and must be provided to EPA for concurrence. It is not intended 

that a public review process (comment period or public hearing) be conducted 

26 
solely for the purpose of determining whether data should or should not be 

, 

. flagged. Instead, the public review process referred to in this guide1ine 

refers to the public review process which is otherwise required for regulatory . 

actions taken in accordance with the Clean Air Act. Although the main purpose 

of the documentation is to support the decision to flag a given piece of data, 

it also provides air quality analysts with background and supporting information 

regarding the events associated with the-data on which the analyst can rely if 

and when the data are needed to make a particular air quality decision. The 

air quality analyst will also be aware of any limitations that should be considered in the use of such data. 

. 

~f 

27 
APPENDIX 

DEVELOPMENT OF CRITERIA FOR EXCEPTIONAL EVENTS 

The purpose of this appendix is to summ ~irize the development history of 

this guide1ine and to assist users in understanding the information contained 

herein. 

The Standing Air Monitoring Work Group I;SAMWG) first addressed the issue 

of exceptional values and data flagging in DE

,

~ cember 1981. Subsequent to that 

time, SAMWG solicited input from EPA Regiona'I Offices and State and local 

agencies to identify those exceptional events, that could have any adverse 

effect on air quality values measured during their otcurrence. The SAMWG also 

solicited input on how air quality measured during the exceptional event should 

be flagged. An initial list of possible excESptional events was compiled based 

on comments by selected,Regional Offices and State and local agencies for 

further consideration. 

I. IDENTIFICATION OF EVENTS 

In general, the events given further coiisideration were grouped into three 

major categories: (1) natural events (meteor°ological and other natural events), 

(2) unintentional anthropogenic events, and (3) intentional anthropogeriic events. 

The events within each major category were as follows: 

1. Natural Events 

(a) Meteorological Events 

o Sustained high windspeeds (PM) 

o Stagnations/inversions (all pollutants) 

` o Unusual lack of precipitation (PM) 

o Stratospheric ozone intrusion (03) 

x 

: 
.' ~ • ' ~ 

(b) Other Natural Events 

o Volcanic eruption (CO 3S02, PM) . 

o Forest fires (CO 3PM) 

., 

o High pollen count (PM) 

2. Unintentional Anthropogenic Events 

o Large accidental structural fires (CO 3PM) 

o Major traffic congestion due to accident or nonrecurring 

obstruction (CO) 

o Chemical spills (S02, NO2, PM, CO) 

o Industrial accidents (S02, NO2, PM, CO) 

3. Intentional Anthropogenic Events 

o Short-term construction/demolition (PM) 

o Sandblasting (PM) 

o High-sulfur oil refining (S02Y 

o Roofing operations (PM, S02) 

p Salting or sanding of streets (PM) 

o Infrequent large gatherings (PM, CO) 

o Soot blowing from ships (PM) 

o Agricultural tilling (PM) 

o Prescribed burning (CO 3PM) 

o Noncompliance--point source (CO 3S02, NO2, PM) 

Those whose comments and suggestions were solicited generally agreed that 

natural events, other than meteorological events, and unintentional anthropogenic events are, by their very nature, exceptional events. The control of , 

emissions from such events is usually not included in the general control 

, 

strategy for a given pollutant, although it is sometimes handled as part of an 

29 
~ s 

a 

' emergency response action immediately after the event has occurred to minimize 

possible adverse health impacts on local res - idents. Reasonable precautions 

would not guarantee against recurrence or that the air quality would not be 

affected by these events in the future. 

Some disagreement was expressed with regard to intentional anthropogenic 

events. Some argued that these events occur routinely and the data therefore 

should not be flagged. Others argued that, although intentional anthropogenic 

events occur routinely, they are exceptional with respect to normal activities 

around a particular monitoring site. Still t,3thers argued that intentional 

anthropogenic events can and should be controlled; they f urther argued that, 

unless these events or activities occur within the immediate vici- nity of a 

monitoring site, they should not be considered as exceptional and the data 

collected during their occurrenceshould not be flagged. 

Finally, some strong disagreement was expressed with respect to two 

meteorological events--stagnations and inversions. Many argue that these two 

events routinely occur. They further argue 'that because these events are 

climatological factors rather than exceptional events, pollutant levels 

measured during their occurrence should not be flagged. 

The list of suggested exceptional events was reviewed and evaluated to 

determine whether each of the events listed shouid be considered exceptional and 

whether other events should be added. The review indicated that this list was 

comprehensive and that no additional events should be considered at this time. 

T Af ter considerable discussion over an extended period of time, a general 

consensus was reached that 15 of the events ;initially considered for designation 

V 

did generally satisfy the criteria for defining an exceptional event. Six of 

the events initially considered {implementing transportation controls, 

30 
14 

stagnation/inversions, high-sulfur oil refining, sootblowing from ships, 

noncompliance--local sources, and unusual lack of precipitation) however, were ' 

finally rejected. The rationale for rejecting these events is summarized 

t 

below. 

II. EVENTS NOT CONSIDERED EXCEPTIONAL FOR DATA FLAGGING PURPOSES 

1. Implementing Transportation Controls 

Transportation control measures are not considered exceptional, and clata 

collected during the implementation of transportation controls should not be 

flagged. If, however, traffic must be temporarily rerouted during the implementation of the transportation control measures or some congestion occurs 

due to initial startup of the transportation plan, the data collected at 

monitors near the rerouted traffic or congestion may be flagged. 

2. Stagnations/Tnversions 

Stagnations and inversions are frequent climatological occurrerices that 

mtjst be considered in evaluating whether a control program is adequate to 

attain and maintain the NAAQS. An inversion is said to occur at a point, or 

through a layer, where temperature increases with increasing height. 20 , 21 

Surface-based inversions are those that extend vertically from the surface to 

some altitude aloft. One study found that surface-based inversions generally 

occur about 32 percent of the time. 22They are usually short-lived and disperse 

shortly after sunrise. Because inversions are expected to occur frequent1y and 

are part of weather patterns, they are not considered exceptional events 'for 

the purpose of flagging data. 

Stagnation episodes are periods of 4 or more days with surface wind speeds 

of generally 4 m/sec or less and no precipitation or frontal passage. In some " 

31 
~ • 

parts of the United States stagnations usuallly persist for an extended period 

of time, and they can affect an entire air Eiasin5 therefore, they are not 

generally considered exceptional for the purpose of flagging data. 

3. Pligh-Sulfu r Oil Refining 

High-sulf ur oil refining refers to the,process of refining crud e oil 

with a sulfur content that is 20 percent or greater than the design capacity 

of the refining operation. Because this is a common practice at many 

refineries, and procedures and control methods are used to minimize S02 

emissions, it is not considered to be an exceptional event for the purpose 

of fl aggi ng data. 

4. Sootblowing from Ships 

Sootblowing f rom ships is a method in which air is used to remove 

deposits that may build up on the walls of the vessel's boiler tubes. This is 

a common practice that is either controlled or limited (in many areas of the 

country) by establishing opacity limits. Betause these activities are common 

and steps can be taken to minimize associated emissions, sootblowing f rom 

ships (like general sootblowing from utility and industrial boilers) is not 

considered an exceptional event for the purpose of flagging data. 

5. Noncompliance--Local Sources 

Limited noncompliance of local sources (:an be expected from time to time 

as a result of process upsets or malfunction -ing control equipment. These 

events are usual ly classified as "upsets" or, "malfunctions" as defined by 

, the applicable State or local agency regulations, or they may be considered 

a violation of applicable emission or opacity limits. If these events are 

caused by upsets or malfunctions, they shoulcl be so noted and reported to the 

appropriate control agency. If they constitute a violation, the appropriate 

32 
~ 

legal remedies will be taken. If legal action is taken, the air quality da.ta 

collected in the vicinity of the source will in all likelihood be used in the 

legal proceedings, and any appropriate limitations associated with the data ~. 

would be reviewed and evaluated as part of the legal process. Because data 

collected during noncompliance conditions have special uses and the source 

is required to notify the State of the upset or malfunction, noncompliance of 

local sources is not considered an exceptional event for the purpose of 

flagging data. 

6. Unusual Lack of Precipitation 

Lack of precipitation in and of itself would not be considered an 

exceptional event because it has very little impact on PM air quality leve'Is. 

Lack of precipitation or drought conditions combined with high winds, however, 

would be considered an exceptional event. Therefore, unusual lack of precipitation is not considered an exceptional event for the purpose of flagging 

data. 

3 

33 
REFERENCES 

1. "Guideline for Interpretation of Air Quality Standards," U. S. Environmental 

Protection Agency, Office of Air Quality Planning and Standards, Research 

Triangle Park, N.C. OAQPS No. 1.2-008 (revised February 1977). 

2. 40 CFR 51.12d, Code of Federal Regulations, July 1, 1984. 

3. Federal Register, Vol. 49, March 20, 1984 pp. 10433-10435. 

4. Clean Air Act as amended August 1977. 

5. Byers, H. R. Generai Meteorology. McGr!aw Hill, New York, New York, 1974. 

6. Anthes, R. A., et al. The Atmosphere. Charles E. Merril Publishing 

Co., Coiumbus, Ohio, 1975. 

7. Federal Meteorological Handbook No. 1, Surface Observations. Washington, 

D.C. 1976. 

8. Dorn, W. L. Meteorology. Third edition. McGraw Hill, New York, 

New York, 1965. j 

9. Bates,• R. L..., and J. A. Jackson. Glossary of Geology. Second edition. 

American Geological Institute, Fall-s Church, Virginia, 1980. 

10. Personal Communication with Linda Farnsworth of the USDA Forest Service, 

Aviation and Fire Management Division, Fire Department, November 1983. 

11. Receptor Model Technical Series, Volume I, Overview of Receptor Model 

Application to Particulate Source Apportionment, U.S. Environmental 

Protection Agency, Office of Air Quality Planning and St andards, Research 

Triangle Park, N C. EPA Publication No. EPA-450/4-81-016a. July 1981. 

12. Receptor Model Technical Series, Volume II, Chemical Mass Balance, U.S. 

Environmental Protection Agency, Office of Air Quaiity Plannirig and Standards, Research Triangle Park, N C. EPA Publication No. EPA-450/4-81-016b. 

July 1981. 

13. Receptor Model Technical Series, Volume III, User's Manual for Chernical 

Mass Balance Model, U.S. Environmental Protection Agency, Office of Air 

Quality Planning and Standards, Research Triangle Park, N C. EPA Publication No. EPA-450/4-83-014. July 1983. 

, 14. Receptor Model Technical Series, Volume :[V, Sunmary of Particle Identification Techniques, U.S. Environmental Protection Agency, Office of Air 

Quality Planning and Standards, Research Triangle Park, N C. EPA Publica- 

. tion No. EPA-450/4-83-018. June 1983. 

34 
15. Guideline on Air Quality Models. OAQPS, U.S. Environmental Protection 

Agency, Research Triangle Park, N C. EPA Publication No. EPA-450/2-78- 

027 (NTIS PB 288-783). April 1978, or subsequent revisions. ' 

16. Regional Workshops on Air Quality Modeling: A Summary Report, U.S. 

Environmental Protection Agency, Office of Air Quality Planning and " 

Standards, Research Triangle Park, N C. EPA Publication No. EPA-450/4- 

82-015, (NTIS PB 83-150573), April 1981. (NTIS documents include 1982 

and 1983 addendums) 

17. Air Pollution Aspects of Aeroallergens (Pollens). National Air Pollution 

Control Administration Consumer Protection and Environmental Health 

Services, Department of Health, Education, and Welf are, September 1969. 

18. Sonti, R. S. Practical Design and Operation of Vapor-Depressuring 

Systems. Chemical Engineering, 91(2):66, January 23, 1984. 

19. An Introduction to Highway Transportation Engineering. Institute of 

Traffic Engineering, 1978. 

20. McIntosh, D. H. Meteorological Glossary. Chemical Publishing, New York, 

1972. 

21. Huschke, R. E. Glossary of Meteorology. American Meteorological 

 Society, 1959. 

22. Geiger, R. The Climate Near the Ground. Harvard University Press. 

1966. 

r 

35 
s ` 

TECHNICAL REPORIr DATA .0 

(Please read lnstructfons on the reverse bejore completing) 

1. REPORT NO. 2. 3. RECIPIENT'S ACCESSION NO. 

EPA 450/4-86-007 

4. TITLE AND SUBTITLE 

Guideline on the Identification and Use of Air Qtiality 

5. REPORT DATE 

July 1906 

Data Affected by Exceptional Events 6.PERFORNNNG ORGANIZATION CODE 

7. AUTHOR(S) S. PERFORMING ORGANIZATION REPORT NO. 

EPA 450/4-36-007 

9. PERFORMING ORGANIZATION NAME AND ADDRESS 10. PROGRAM ELEMENT NO. 

U.S. Environmental Protection Agency 

Monitoring and Data Analysis DlvlSlon 11.CONTRACT/GRANT NO. 

Monitoring and Reports Eranch 

Monitoring Section, RTP, iJC 27711 

12. SPONSORING AGENCY NAME AND ADDRESS 13. TYPE OF REPORT AND PERIOD COVERED 

Technical guideiine 

Same as 9. 14. SPONSORING AGENCY CODE 

15. SUPPLEMENTARY NOTES 

16. ABSTRACT 

This guideline is intended to provide information to•State and iocal air 

pollution control agencies concerning the flagging of air quality data affected 

by exceptional events. The guidance defines exceptional events, establishes 

unifo.rm criteria and procedures for flagging air quality data, and provides a 

mechanism for allowing consideration of excludirng flagged data. 

17. KEY WORDS AND DOC-UMEN'T ANALYSIS --- 

a. DESCRIPTORS b.IDENTIFIERS/OPEN ENDED TERMS C. COSATI E•ield/GtOup 

Exceptional events 

Data flag 

Air quality data 

Excluding flagged data 

18. DISTRIBUTION STATEMENT 19. SECURITY CLASS (TItlsReport) 21. NO. OF PAGES 

Unlimited Unc'lassified 

20. SECIJFIITY CLASS (This page) 22. PRICE 

Unc•lassif ied 

EPA Form 2220-1 (Rav. 4-77) PREVIOUS EDITtON 15 OBSOLETE 
' i